During winter/cold weather hikes/camping,I wear silk for my 1st layer with merino wool socks/gloves,Merino wool or fleece for the 2nd layer,& 3rd usually a Polyester or Nylon shell/pants of some kind,having a wool parka/mittens for back-up stowed in pack.Synthetic mummy bag(hollow-fill) for sleeping under my vulcanized military poncho w/woobie.I used to have a Woods down bag many yrs ago,It got wet twice for the many yrs I used it,I can still recall those 2 trips vividly!As I age,I still have no problem humping 40+lbs as a standard,a small price for comfort-IMHO!If you are wearing wool while sleeping,there is no need for feathers.